Manganese

What is it?

Manganese is an essential trace element for humans. The average adult body contains between 12 and 20 mg with the highest concentrations in the bones, liver, kidneys and heart.

What it does in the body

Manganese appears to be involved in many enzyme systems, although its functions are not well understood. It acts as a co-factor for enzymes necessary for energy production and is involved in glucose metabolism, the stimulation of glycogen storage in the liver, protein digestion and cholesterol and fatty acid synthesis. It is also necessary for the synthesis of DNA and RNA.

Manganese is necessary for growth, maintenance of the nervous system, the development and maintenance of healthy bones and joints, the formation of blood clotting factors, female sex hormone function and thyroid hormone function.

Superoxide dismutase

One form of the antioxidant enzyme, superoxide dismutase, contains manganese. Proper function of this enzyme helps protect against free radical damage. (See page 417 for more information.) Laboratory studies have shown that it can protect brain cells from the type of damage seen in stroke and Alzheimer's disease.¹ It may also help to protect against liver damage. Manganese superoxide dismutase levels are higher in alcoholics and may help to protect against oxidative damage by alcohol.²

Absorption and metabolism

Only 3 to 5 per cent of dietary manganese is absorbed. After absorption, manganese is transported to the liver.

Deficiencies

The first report of a manganese deficiency occurred as recently as 1972 in a man who lived for four months on a manganese-free diet. Symptoms include dizziness, bone problems, reduced growth of hair and nails, weakness, hearing problems, weight loss, abnormal gait, and skin problems. In children, severe deficiency may lead to convulsions, paralysis or blindness.

Marginal deficiency may arise when processed or refined foods form a large part of the diet. Marginal intake of manganese may increase loss of calcium from bone, increasing the risk of osteoporosis. Diabetics often have low manganese levels which may contribute to abnormal blood sugar regulation and decreased pancreatic cell function. Manganese deficiency appears to lead to abnormal glucose transport and metabolism.³ Manganese deficiency may also play a role in epilepsy and infertility.

Recent research in rats suggests that manganese deficiency may lead to artery damage as a manganese-dependent enzyme is involved in the formation of arterial connective tissue. Damage to artery wall structure can promote the binding of harmful LDL cholesterol and the formation of atherosclerotic plaque.

Sources

Good sources of manganese include cereals, spinach, wholemeal bread, nuts, pulses, fruit, dark green leafy vegetables, root vegetables, tea and liver. As much as 86 per cent of the manganese content is lost when flour is refined and 89 per cent is lost when sugar is refined.

Food	Amount	Manganese (mg)
Wheat bran	½ cup	3.17
Brown rice, cooked	1 cup	1.68
Chickpeas, cooked	1 cup	1.60
Spinach, boiled	1 cup	1.60
Almonds	½ cup	1.53

Buckwheat	½ cup	1.05

Lentils, cooked	1 cup	0.93
Lima beans	1 cup	0.92
Kidney beans, cooked	1 cup	0.80
Green peas	1 cup	0.80
White rice, cooked	1 cup	0.71
Wholewheat bread	1 slice	0.65
Wheat bran bread	1 slice	0.60
Carrots, cooked	½ cup, slices	0.56
Kale	1 cup, chopped	0.51
Tea	1 cup	0.49
Raisins	1 cup	0.48
Prunes, dried	1 cup	0.36
Snap beans, boiled	1 cup	0.35
Beef liver, fried	85g	0.36
Sweetcorn, boiled	1 cup	0.36
Beets, boiled	½ cup, slices	0.26
Brazil nuts	6-8 nuts	0.22

Recommended dietary allowances (RDA)

Suggested daily intake ranges from 2 to 5 mg. Such amounts are easily obtained from diets high in whole grains and vegetables.

Supplements

Manganese supplements are available in various forms including amino acid chelates, manganese sulfate and manganese gluconate. Manganese most often occurs in multivitamin and mineral supplements in doses of 1 to 9 mg.

Toxic effects of excess intake

Toxic effects from oral ingestion of manganese are very rare and include lethargy, involuntary movements, changes in muscle tone and posture, and coma. Toxic effects known as 'manganese madness' have been observed in manganese miners. Symptoms include unaccountable laughter, impulsiveness, inability to sleep, violent acts, delusions and hallucinations.

Therapeutic uses of supplements

Inflammation

Manganese supplements have been used to treat inflammation, strains and sprains. Activity levels of the enzyme, superoxide dismutase, have been raised by manganese supplementation which may protect against the oxidative damage seen in inflammatory disorders such as arthritis.⁴

Other uses

Manganese supplements have also been used to treat schizophrenia, epilepsy, osteoporosis, multiple sclerosis and anemia. Manganese may be useful in the treatment of diabetes through effects on glucose metabolism.

Interactions

Interactions with other nutrients

Manganese may inhibit the absorption of copper, iron and zinc. Calcium, iron, copper, manganese and zinc compete for absorption in the small intestine and high intake of one of the minerals reduces the absorption of the others. Magnesium may substitute for manganese in certain conditions when manganese is deficient. Manganese functions with vitamin K in the formation of blood clotting factors.